Systems for the application of liquid coating materials, adhesives and the like include liquid dispensing devices such as spray guns which are supplied with liquid from a pump operatively connected to a tank or other source of the liquid. In order to control the pressure at which the liquid is supplied to the spray guns, pressure regulators are commonly interposed between the pump and spray guns.
One type of pressure regulator used in applications of this type includes a regulator body formed with a liquid passageway having an inlet which receives liquid from the pump and outlet which discharges the liquid to at least one spray gun. A poppet valve or similar flow control device is carried by a thin, flexible diaphragm within the regulator body. In response to flexing of the diaphragm, the poppet valve is movable relative to a valve seat located within the liquid passageway to control the pressure at which the liquid is discharged from the outlet of the passageway to the spray gun. Many pressure regulators of this type are pneumatically operated, i.e., a pneumatic panel or other air supply device transmits operating air to the side of the diaphragm opposite the liquid passageway to flex the diaphragm and thereby adjust the poppet valve to the desired position relative to the valve seat within the liquid passageway. The thin, flexible diaphragm is highly responsive to the flow of operating air from the pneumatic panel, and thus good control of the pressure of the liquid discharged from the pressure regulator can be obtained.
One problem with pneumatically operated, diaphragm-type pressure regulators is the damage to the pneumatic panel or other air supply device which can be created in the event of a failure of the diaphragm. Because the liquid flowing through the passageway in the pressure regulator is located on the side of the diaphragm opposite the operating air, a rupture or leak in the diaphragm can result in the flow of liquid past the diaphragm and then upstream from the pressure regulator into the pneumatic panel. The pneumatic panels are expensive units and can be severely damaged by the back flow of liquid therein.
One proposed solution to this problem has been to incorporate redundant or additional diaphragms within the pressure regulator so that in the event of the failure of one diaphragm, a second or third diaphragm is available to block the escape of liquid upstream to the pneumatic panel. But pressure regulators employing two or more diaphragms are relatively expensive and complicated. In addition, such pressure regulators provide no means to indicate if a rupture, leak or other failure of the diaphragm(s) has occurred.